2 Answers
2

If you need to switch frequently between various connections, have a look at this:

NetSetMan allows you to quickly switch between pre-configured
network settings. The program is ideal
for people on the road, who frequently
connect to different networks and need
to update or reconfigure their network
settings each time. NetSetMan
eliminates the need for manual
configurations, you can simply create
different profiles to store your
network configuration, and then switch
between them with the click of a
button. NetSetMan can apply
configuration settings for IP address
Subnet Mask, Default Gateway, WiFi,
Printer, DNS servers and more. The
free version is limited to 6 network
profiles, which is more than enough
for personal usage - commercial usage
requires a license.

or this:

IP Organizer 2 does what it says on the tin, and it does it for free. pretty much like NetSetMan, it allows you to switch between multiple network profiles (unlimited). NetSetMan features more functions but is only free for private use while IP Organizer 2 is free as in free beer.

If you have a router available, you can set it up to manage the connection for you. It will then be able to automatically provide you a DHCP lease when your computer starts up -- no fiddling with usernames and passwords.

If you want to use various networks, Net Profiles can make connecting to each one a breeze: